Air filters are used in vehicles to provide clean air for induction into the engine system. Air filter may become clogged due to accumulation of dirt and debris. Clogged air filter may increase the intake air pressure drop and restrict air flow into the engine. The restriction of air flow may affect engine performance and efficiency. In order to replace or clean the clogged air filter, a status of the air filter can be regularly diagnosed, and indicated to the operator.
Attempts for diagnosing air filter status include diagnosing the air filter based on a pressure drop across the filter. One example approach is shown by Pago et al. in U.S. Pat. No. 5,606,311. Therein, pressure drop across the air filter and corresponding air flow are measured during engine operation, filter restriction is then estimated by comparing the measured pressure drop to a referenced pressure drop.
However, the inventors herein have recognized potential issues with such approach. As one example, air filter diagnosis based on a pressure drop during engine operation may not be accurate due to low signal to noise ratio. Specifically, the signal amplitude of the pressure drop may be low, as the pressure drop may not be significant relative to the sensor sensitivity even for a clogged filter depending on the operating conditions of the vehicle. Further, the reciprocating operation of the engine may introduce high noise. As a result, Pago's method may generate false positive results, which may alert the driver that the air filter requires replacement before it is necessary. Moreover, in hybrid vehicles, engine running time may be limited. Diagnosing air filter status during engine operation may not be frequent enough to identify air filter clogging. Additional, the duration of stable engine operation in a hybrid vehicle may not be long enough to obtain reliable pressure measurements.
In one example, the issues described above may be addressed by a method comprising: during engine off, opening a high pressure exhaust recirculation (HP-EGR) valve; flowing air through an air filter by actuating a motor coupled to a compressor; sensing an air pressure; and indicating status of the air filter based on the air pressure. In this way, air filter clogging may be timely and robustly detected.
As one example, in an engine system equipped with an electric boosted device, during engine off, a motor coupled to the electric boosted device may be operated to flow ambient air into the engine system through the intake air filter. One or more valves, such as a HP-EGR valve, may be opened to flow the air further from the air filter, bypassing the cylinder, to an exhaust passage. Air filter status may be diagnosed based on pressure measurement related to the air flow through the air filter. As one example, the pressure may be a pressure drop across the air filter. As another example, the pressure may be a pressure downstream of the air filter, in the direction of the air flow. By flowing the air from the filter to the exhaust passage bypassing the cylinder, the air may flow through the engine system with little resistance. As such, the pressure measurement may accurately reflect flow restriction caused by air filter clogging. Possible interferences caused by other components of the vehicle system on the measurement may be avoided. Further, the duration for conducting the air filter diagnosis may be reduced, as the air flow may be fully controlled and quickly stabilized via operating the electric boost device. By diagnosing the air filter during engine off, the air filter status may be frequently checked during automatic engine stop-start, avoiding noises introduced by the reciprocating engine operation. Moreover, by utilizing the motor coupled to the electric boosting device for air filter diagnosis, the diagnosis may be performed with existing engine components.
As another example, during a first condition, a first air pressure may be measured while flowing air in a first direction from the atmosphere to the compressor through the air filter. Subsequently, a second air pressure may be measured while flowing the air in a second direction, opposite to the first direction, from the compressor to the atmosphere through the air filter. The air filter may be diagnosed based on the first and the second air pressures. By flowing the air in a reversed direction, the air filter may be diagnosed when the HP-EGR valve is not present in the engine system. In one embodiment, the first condition may be during engine operation, and the second condition may be during engine off. The motor may be actuated to flow the air through the air filter in a second direction during engine off, responsive to the first air pressure measured during the engine operation. For example, the first air pressure may indicate the possibility of air filter clogging, and further diagnosis during engine off may increase accuracy of the diagnosis.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.